I teach a course preparing students for college-level writing. In one writing task, the students need to read a passage written by one author, listen to an audio recording by another (who disagrees), then essentially describe and compare the two differing ideas. The writing typically fits into patterns like this:

White says the sky is blue, but Torres says it is not.

While White argues that the sky is blue, Torres argues that it is not.

According to White, the sky is blue. Torres, contends, however, that it is not.

White claims that the sky is blue. Torres, on the other hand, presents the case that it is not.

In each of the examples above, there are markers which help the reader to understand that an apposing view is being presented:

..., but...

While......,...

..., however,...

..., on the other hand,...

According to Wikipedia, these are all examples of conjunctions, however, I need a more specific term to refer to these, meaning something like "conjunctions that tell readers that two contrasting ideas are presented" or simply "conjunctions that tell readers that two somewhat different ideas are presented". In other words, I need a term with this meaning, excluding the other types of conjunctions listed in Wikipedia's entry.